Letters and words alone have no significance—it's when someone strings them together that they take on meaning. Chip Kidd, in his introduction to Just My Type, says,
"Let's consider the English alphabet: twenty-six purely abstract symbols that in and of themselves mean absolutely nothing, but when put together in the right combinations can introduce into the heads of readers an infinite variety of sounds, smells, tastes, feelings, places, people, characters, situations, feelings, ideas."
Without a purpose, words become meaningless. With a purpose, Chip adds,
“Entire universes are born out of just a few sentences, and can be just as quickly destroyed.”
Writing well is creating a world that your reader can enter without trying, and communicating an idea so clearly a child could explain it from your description. To give words successful purpose, a writer must know a) what they want to say and b) how to say it.
The purpose without the talent is inarticulate passion.
The talent without the purpose is empty vocabulary.